Technicality

Okay, I guess it isn't a Punch Cannon, it's a Punch Tank that has a cannon also.

I present from the Art of World of Warcraft panel, the Heavy Mortar. I quote Eric Browning (Lead Prop Artist) who you can hear around the 5:27 mark of the panel video, if you have the virtual ticket.

It punches! It's a tank and it punches! Cause it's not enough to shoot somebody, you can punch 'em.

(It's a Punch Cannon)